The invention concerns a collapsible U-channel, in particular made of cardboard, its fabrication method and equipment to implement said method.
The use of U-channels in particular for packing is known.
The European patent 0,411,045 for instance describes a packing container to pack long articles and comprising two U-channels nested in each other.
To manufacture such structures, it is known in particular to adhesively paste paper or cardboard strips and optionally to cover them with a wrap made for instance of a strong material such as cardboard.
Again is it known to flame-laminate composite cardboard-polyolefin strips to implement diverse structures and in particular U-channels.
As regards the fabrication methods for such U-channels based on strong strips, the only known method consists in bonding the strips to each other while flat and then, using a sequence of shaping stations, to make two main folds on the planar strip product and to carry out the folding operation progressively so as to ultimately arrive at a structure with a U cross-section.
When this method is carried out, the adhesive layers rapidly bond to each other strongly either on account of the action of the adhesive which is used for cardboard strips or on account of the flame-heated polyethylene in the case of composite strips of cardboard and polyethylene.
The U-channel made by this technique is rigid and the angle subtended between the base of the U and each of its two legs in general is close to 90xc2x0 and cannot be modified when the adhesive is setting. Following manufacture, a substantial modification of this angle and spreading the legs in a direction perpendicular to the longitudinal U-channel axis entails degradation of said channel by delaminating its constituent strips and consequently makes this channel useless.
The U-channels made by this technique can be stacked only with difficulty, contrary to the case of the L-structures. The sole known way to stack them compactly consists in stacking them pairwise with one channel inverted over two others, that is each channel straddles one of the legs of another.
It is easily understood that the rigid channels made by these procedures entail high shipping and/or storage costs after they have in general been put on pallets, considering the substantial volume taken up by such stacks in relation to the actual material involved.
Unit shipping costs will be the larger the larger the dimensions of the U-channels.
The objective of the present invention in particular is to remedy such drawbacks and to optimize stacking these U-channels by eliminating or reducing as best possible the dead volumes regardless of the dimensions of the U-channels.
In order to optimize channel stacking in this manner, the invention proposes a U-channel, comprising a base and two side legs, which is characterized in particular in that it comprises a longitudinal folding line at its base, said line in particular being situated near the median base line in such manner that said base is able to fold inward while at the same time the legs flare outward in such a way that the structure may assume a substantial W-shape, thereby facilitating in particular its storage and/or its shipping.
Another objective of the invention is a manufacturing method for such a U-channel, where this method is characterized by including a stage forming a longitudinal folding line in the base of the structure during the fabrication of this U-channel.
Advantageously the folding line is implemented on a planar, semi-finished product before the U-channel legs will be made by folding.
As regards the manufacture of a U-channel based on bonded strips, in particular made of cardboard or of cardboard-polyolefins composites, the invention proposes implementing this folding line by a grooving operation.
Illustratively this grooving operation may be carried out by impression, without removing material, or by milling with removal of material, or by incision on the inside of the base.
In one embodiment of the invention, the folding line is reinforced at least on one of the base sides by an apposed reinforcing tape.
In the latter case and as regards an incised groove, the invention places the reinforcing tape above the incision by forming at this site a pleat to allow folding the U-channel.
In another embodiment of the invention, the reinforcing tape wraps a large part of the structure except at least one portion of one of the base""s sides of said structure at the site of the folding line.
The invention furthermore proposes another method which is characterized by joining two L-structures that are abutted to each other by their legs by a junction tape affixed on said legs.
Lastly the invention also proposes equipment with which to carry out the above methods and characterized in that it comprises beyond the known U-channel manufacturing stations also a grooving station that shall longitudinally groove that portion of the structure that shall constitute the base of said U-channel.